A. Field of the Invention
The present invention relates generally to an apparatus for cooling a cylindrical film in producing a thermoelastic resin film by inflation method, or more precisely, the variable-type bubble water cooling apparatus by which the upper and lower ends of numbers of curved cooling pipes are rotatably supported, the cooling water being supplied to the pipes, and the diameter of enveloping circle formed by these curved cooling pipes at a determined horizontal position is varied by relatively rotating the upper and lower ends of support members of pipes.
B. Description of Prior Art
In an inflation method for manufacturing films or bags of thermoelastic resin, a bubble which is inflated in a cylindrical form with air or water must be rapidly cooled and then taken up by a roll. An outline of inflation molding is given with reference to FIG. 1. Thermoelastic resin pellet thrown into an extruder 12 from a hopper 10 is heat melted and extruded by the extruder and, passed through a circular die 14 and inflated by a compressed air, becomes a cylindrical film, in other word, a bubble 16. The surface of bubble 16 is cooled by water or air cooling means 18 and put between and made narrower by stabilizing plates 20 and nip rollers 22, is taken up by rollers (not shown), thus becomes flat film or bag. The reason for utilizing water or air cooling means 18 in inflation method is, although different according to the kinds of resins, to hasten a molding speed, to increase transparency of bubble 16 and to add the intensity of bubble 16. (For example, in case of linear low density polyethylene, such cooling means is utilized in order to obtain high transparency. In case of polypropylene, for obtaining high transparency as well as increased intensity.) In these cooling means, air cooling means have defects that the transparency of bubble can not be increased, as the bubble is cooled only gradually (For example, double staged air cooling means must be employed.). In addition, the bubble is vibrated by air flow, therefore, such air cooling means are not within the scope of the present invention. On the other hand, the babble is rapidly cooled near its frost line by the water cooling means which directly contacts with the bubble. Accordingly, the water cooling means are advantageous that the transparency of bubble can by far be increased by hastening its crystallization.
In the Japanese published patent specification No. 46-37111, prior art water cooling means are disclosed, as shown in FIG. 2. The water cooling means comprise a plurality of semi-circular or horseshoe-shaped pipes 24 by which are formed an annular water cooling ring whose inner diameter can be varied. But, the inner diameter of the combined water ring can not be varied uniformly with regard to its radius direction, accordingly, many kinds of rings must be prepared for attending the change of bubble size. The unevenness of thickness of bubble is caused due to the irregularity of cooling effect, as the contact position of rings to bubble lacks uniformity. Further, scratches to the bubble is caused, as the passing bubble is caught by the ring. In conclusion, the prior art water cooling means are not adequate for cooling the bubble uniformly.